Magnetic resonance imaging (MRI) is a method of producing graphic images of a three-dimensional object as a result of the excitation and relaxation of certain nuclei in various chemical environments. Nuclei of certain atoms, in particular those having an odd number of protons (charged) and neutrons (uncharged), and usually, more particularly, hydrogen, which has only one proton and no neutrons, are considered to “spin”. Spinning of these charged particles, i.e. circulation of the net charged particles, generates a magnetic moment along the axis of spin, so such nuclei act as tiny bar magnets. When an object to be imaged that contains hydrogen nuclei is placed in a powerful magnetic field, the magnetic moment of the protons are aligned in a particular manner with the applied magnetic field, either with (the field (a more stable configuration) or against the external field. Some energy is needed to change this alignment. Just how much energy is required depends on the strength of the field and the frequency of radiation needed to change the alignment. In Nuclear Magnetic Resonance (NMR), the radiation frequency is kept constant and the applied magnetic field is varied until at some point the energy required to change the alignment of the proton matches the energy of the radiation. At this point, absorption occurs and a signal can be observed and measured. The local chemical environment of the nuclei, as well as surrounding nuclei, will change the effective field strength (and hence the actual applied field strength required) to produce this effect. Chemical environments can also change over time, so the resulting NMR spectrum can be changed as well: absorption peaks can change and broaden in response to time scales on how rapidly and how long fields are applied, how much coupling takes place to neighboring protons, and how quickly and how much change takes place in the local chemical environments. Excitation and relaxation spectra can be complicated: T1 (spin-lattice) and T2 (spin-spin) relaxation times are often monitored for different magnetic pulsing sequences, which nowadays are specified in software and control systems. (To image the object in MRI, magnetic gradients are applied, with the magnet focused on a specific part of anatomy. By applying these gradients, spatial positions are encoded within the phase of the signal of the applied magnetic gradients. These spatially-encoded phases (spatial frequencies) are then recorded in a two- or three-dimensional matrix. Images are created from the matrix using Fourier transform methods. Improvements in computational and image analysis techniques, together with developments in Nuclear Magnetic Resonance (NMR) technology (e.g. magnetic pulsing and echoing techniques) have driven the rapid development of MRI.
The MRI technique is safe, non-invasive, and generally preferred by patients over other imaging techniques because the patients can usually lie down comfortably and remain fully clothed. Physicians prefer MRI over other imaging techniques like ultrasound and X-rays, because there is no ionizing radiation with MRI and because these latter techniques, while valuable, provide less geometric detail and less specificity than MRI. Magnetic field strengths are too low to cause significant health or safety problems. In fact, MRI is becoming less expensive, more accurate, more precise, and easier to interpret. New MRI systems continue to develop at a rapid pace and are widely available in hospitals, medical schools, doctor's offices, and even rural medical clinics.
In general, MRI has been used to diagnose a wide variety of internal disease states. Because the image responds mainly to the nuclear spin states associated with hydrogen nuclei in water and surrounding (and possibly changing) local chemical environments, it can provide information concerning fluids that various anatomical structures contain. By changing MRI pulsing and echoing parameters, a change in grey scale can be produced, to allow one anatomical feature with one chemical environment to be easily distinguished from another. MRI can provide physicians with views of internal organs, bone structure, muscle tone, fluid, and the relative sizes and shapes of products of disease states such as tumors, cysts, clots, and so on.
Pelvic anatomy in both male and female subjects has been studied using MRI techniques. Detailed pictures have been published to provide physicians and other medical practitioners with information and sketches related to key anatomical structures in the pelvic region. Owing to the amount of fluid (urine) present, the bladder is especially easy to see by MRI, typically appearing as white or black in a grey scale image. Other tissues and organs are less easily seen: experts are often needed to interpret complicated anatomical MRI images. One object that can be readily identified when present in a woman's pelvic region using MRI is a tampon. Current methods of using MRI to study tampons in vivo, however, lack precise detailed methods and processes for obtaining realistic measurements of female anatomy and tampons and for assessing performance of the tampons with respect to the female anatomy.
Based on the foregoing, it is an object of the present invention to provide a method for using MRI to study the behavior of tampons in vivo, the resulting images being analyzed to assess tampon functionality in a woman's body.